1. Field of the Invention
The present invention relates to a high-density recording medium, and more precisely to a recording medium having the recording layer containing spherical grains that include inorganic grains.
2. Description of the Related Art
Magnetic recording technology, which is a typical technology for recording media, has some excellent technical advantages which other recording systems do not have. Characteristic advantages thereof are that it allows repeated use of recording media, it facilitates digitization of signals for easy combination with peripheral appliances thereby allowing easy system construction, and it allows easy correction of signals. Having such advantages, magnetic recording technology is therefore widely utilized in various fields including video, audio, computers, and the like.
In order to allow practical use of digital recording systems that realize both improved sound quality and image quality for information data, and further development of image-recording systems suited for high-definition TV, magnetic recording media which enable recording and reproduction of even shorter wavelength signals than those for conventional systems and which ensure good reliability and durability even when a relative speed of the recording medium with respect to a head on which they run is elevated, are presently desired. Desire for development of large-scale digital recording media capable of storing larger amounts of data for use in computers is also increasing.
Given the situation described above, there is demand for microfabrication of recording cells, which are the information-writing units in such recording and reproduction devices and recording media. However, there are often problems in that recording in such microfabricated cells may be unstable and generate noise due to the interaction of magnetic grains in the cells.
To solve the problems described, a magnetic recording medium has been proposed in which magnetic grains on a substrate are microfabricated and are isolated from other grains (S. Y. Chou, et al., J. Appl. Phys., 76 (1994), pp. 6673-6675).
Japanese Patent Application Laid-open (JP-A) No. 10-320772 discloses a method for producing such a magnetic recording medium in which the magnetic grains are isolated from other grains. The method comprises using fine particles, which serve as a mask, are two-dimensionally aligned on a substrate, and have a diameter of from a few nanometers to a few micrometers, to thereby fabricate the intended magnetic recording medium in which the magnetic grains have a reduced grains size distribution and are isolated from other grains on the substrate. However, the method requires additional steps of reactive ion etching and mask vapor deposition, and is therefore inevitably expensive.
JP-A No. 2000-48340 discloses a method that comprises preparing, in a solvent containing an organic stabilizer, a solvent dispersion of magnetic grains, which are produced separately and which have a substantially uniform grain size such that a standard deviation in grain size is smaller than 10% of a mean grain size thereof, then applying the thus-prepared dispersion onto a substrate and evaporating the solvent to thereby form, through such wet chemical treatment, a layer of the magnetic grains, which are coated with the organic stabilizer and are substantially uniformly spaced apart from neighboring ones on the substrate. In the method, the organic stabilizer is subsequently removed by dry vacuum treatment carried out in a plasma reinforced CVD device, and then a protective film is formed on the magnetic layer through treatment in the plasma reinforced CVD device or a reactive sputtering device.
However, the method still requires the complicated steps of preparing magnetic grains having a substantially uniform grain size with no aggregation, then coating the magnetic grains with an organic stabilizer through wet chemical treatment, and finally removing the organic stabilizer in a dry vacuum system. In addition, in the method, control of a distance between grains depends on the organic stabilizer used. Therefore, another problem with the method is that it requires a specifically controlled condition for forming the layer of the two-dimensionally aligned magnetic grains on the substrate.
JP-A No. 2001-167431 discloses another method of forming a layer of magnetic metal grains on a substrate, which comprises applying a dispersion of magnetic metal grains onto a substrate by of spin coating to thereby embed the magnetic metal grains in recording bits that are formed in the substrate through semiconductor lithography. According to this method as well, it is necessary to produce magnetic grains that have a substantially uniform grain size with no aggregation. Another problem with the method is that it is specifically defined by the semiconductor lithography required to form the recording bits in the substrate.
JP-A Nos. 2001-184620 and 2001-184744 disclose still another method of fabricating a recording medium with recording grains being spaced apart from neighboring ones in a controlled manner, which comprises coating information-recording grains having a substantially uniform grain size with a specific organic material that interacts with the grains to thereby specifically isolate the thus-coated grains from each other.
However, the method is still problematic in that it requires troublesome production of information-recording grains having a substantially uniform grain size, and control of a distance between grains depends on a type of organic stabilizer used. Therefore a condition for forming a layer of two-dimensionally aligned grains is specifically defined. Further, in the method, it is considered preferable to etch the two-dimensionally aligned grains in the formed layer to some degree through reactive ion-etching treatment to thereby space the neighboring grains apart from each other. Thus, the method involves various problems, such as requiring troublesome additional steps.